Our project centers around a new cell-type specific (fibroblast) surface antigen recently discovered by us. This antigen (SF antigen) is present in normal but not in Rous sarcoma virus transformed cells, has a uniquely high turnover rate, is shed from the cell surface and appears in the circulation as a novel type of serum protein. These interesting biological properties, especially the loss of the antigen from transformed cells, which appears as a specific major alteration of plasma membrane suggest that molecular studies this antigen may contribute to our knowledge on the mechanisms of malignant transformation and maintenance of the normal phenotype. The possibility of identifying and purifying the SF antigen using specific antibodies and its presence in cultured cells makes feasible detailed and well controlled studies at molecular level, a situation not often encountered with membrane proteins and antigenic changes that occur in malignant transformation. We plan to work with the following aspects of structure and expression of this antigen: - Properties such as molecular weight, polypeptide chain and sugar composition of the various forms of SF antigen. - Quantitative and topographical alteration of the chicken SF antigen in transformation, different phases of cell cycle and of growth control. - Possible association between the loss of SF antigen and appearance of Con A agglutinability. - Possible involvement of circulation of SF antigen in maintenance of immunologic tolerance to fibroblasts. - Function of the SF antigen either in the cellular or extracellular form in intercellular attachment and recognition. - Characterization the analogous system in human fibroblasts and serum and its loss from transformed fibroblasts. Search for an analogous malignancy associated surface alteration in other cell types. We plan to examine the human glia-glioma and hepatocyte-hepatoma system. - Use of SF antibodies in identifying and erradicating fibroblasts from primary human tumor cell cultures. - The quantity and/or molecular properties of SF antigen in human serum (altered in tumor patients)?